This application is related to commonly assigned copending applications: Ser. No. 239,095, now U.S. Pat. No. 4,365,687; and Ser. No. 239,284, filed Mar. 2, 1981.
In the prior art, industrial trucks such as lift trucks have been provided with controllers actuated by manually operated selector levers for placing the electric traction motor in forward or reverse drive or in neutral or park conditions. In general, such prior art devices utilize rotary cams for actuating a directional control switch, brake control means and speed control means. For example, the Hastings U.S. Pat. No. 3,179,198 discloses a controller for lift trucks with a single, manually operated lever for both direction and speed control. This controller includes a first cam and cam follower for actuating a direction control switch to either forward or reverse position depending upon the direction of motion of the manual control lever. It includes an additional cam and cam follower for controlling the release of the brakes upon movement of the control lever in either direction. It includes another cam, which is driven unidirectionally by the first cam, and has a cam follower which controls the vehicle speed through a series of sequentially actuated switches. The Ulinski U.S. Pat. No. 2,267,381 also discloses a combined direction and speed controller for an electric lift truck. The controller of this patent uses electrical contactors of the drum type.
It is also known in the prior art to provide electric lift trucks with automatic braking when the operator dismounts or leaves his operating station on the vehicle. The Hastings U.S. Pat. No. 3,179,198 discloses a brake system in which the brake is applied when the operator dismounts and removes his foot from a pedal on the floor. A failsafe brake is described in which the brake is spring applied and pressure released. The Guhl et al U.S. Pat. No. 4,004,665 relates to a transmission and parking brake controller. The selector lever covers a range of forward drive speeds and reverse drive speeds together with neutral and park positions. When the selector lever is placed in park position, by a transverse movement of the lever, the fluid pressure to the brake is vented and the brake is spring applied. This system is manually actuated and not responsive to the operator dismounting from the vehicle. The Boyajian U.S. Pat. No. 3,507,350 discloses an electric lift truck with means for preventing vehicle drive unless the operator's seat is occupied. The system of this patent uses a seat switch and relay means for disabling the power circuit unless the seat switch is closed and the drive selector is initially in the neutral position.
A general object of this invention is to provide an improved controller for the traction motor of an electric vehicle and to overcome certain disadvantages of the prior art.